Position measuring apparatus with multiple scanning locations

Abstract

A measuring device is provided in which a graduated plate is scanned in at least two scanning locations. The scanning signals from the different scanning locations are transmitted to a testing circuit which determines whether the phase displacement between the scanning signals exceeds a limit value. If the limit value is exceeded, one of the scanning locations is weighted higher than the other. The weighting is implemented by increasing the components of the signals from one scanning location while decreasing the components from the signals from the other scanning location.

We claim: 
     
       1. In a position measuring apparatus including a measurement embodiment, and a plurality of scanning devices arranged to scan said measurement embodiment at a plurality of different scanning locations, each of said scanning devices generating scanning signals corresponding to each of said scanning locations, wherein the improvement comprises: evaluating circuit means including a testing circuit for evaluating said scanning signals from said scanning locations and detecting the occurrence of predefined conditions from said scanning signals; and   weighting means for unequally weighting said scanning signals from said different scanning locations when said testing circuit evaluates said scanning signals and detects the occurrence of at least one of the following conditions (a) the phase displacement between said scanning signals from said different scanning locations exceeds a predetermined tolerance range, and (b) the amplitude of the sum of the signals from said different scanning locations exceeds a predetermined tolerance range.   
     
     
       2. The position measuring apparatus of claim 1 wherein weighting means comprises a control member. 
     
     
       3. The position measuring apparatus of claim 2 wherein said control member includes a control amplifier responsive to said testing circuit, and a plurality of summing elements for providing the sum of the signals from said different scanning locations and wherein said summing elements are further responsive to said control amplifier such that said summed signals are weighted in response to said control amplifier. 
     
     
       4. The position measuring apparatus of claim 1 wherein said testing circuit includes a plurality of difference generators for providing the difference between said scanning signals from said different scanning locations, and a value-generating component responsive to said difference generators. 
     
     
       5. The position measuring apparatus of claim 4 wherein said value-generating component comprises a full-wave rectifier. 
     
     
       6. The position measuring apparatus of claim 3 wherein said summing elements comprise electrically adjustable resistors. 
     
     
       7. The position measuring apparatus of claim 1 wherein said weighting means comprises means for controlling energy supplied to said scanning elements.